Method of coating stainless steel tube with copper



8,1970' l SJ-.IANNQNE 3,546,080

' METHOD 0F COATIJNG S'TINLESS STEEL TUBEWITH COPPER Original Flled Sept. 26, 1966 .n a--nc--nn- Jlllllll/llllllJlL/lljlll Il l lll/ll l l /l/l/l//Jll/ [Il] INVENroR amzze/J/dfz/za/ze Y BY,

ATroRNEY United States Patent O U.S. Cl. 204- 5 Claims This application is a division of my application Ser. No. 575,416, filed Aug. 26, 1966.

The present invention relates to a new and novel copper coated stainless steel tube and method of manufacture thereof; and more particularly to composite tubing for use as a substitute for copper tubing.

The present invention is especially adapted for use in applications where copper tubing is ordinarily employed, as for example in the plumbing eld wherein copper tubing is extensively used due to the facility with which it can be connected with the littings required in ordinary plumbing practice.

The copper coated stainless steel tube of the present invention affords a number of important advantages over conventional copper tubing. The tubing of the present invention is considerably less expensive than ordinary copper tubing and is of no greater over-all size. Additionally, the tubing of the present invention meets all standards required of copper tubing, and yet the invention tubing is considerably lighter than comparable copper tubing.

The utilization of an inner layer of stainless steel is highly advantageous where the tubing is used as a conduit means for corrosive liquids. For example, water which is high in chlorides or fluorides and which has a pH on the acid side will pinhole copper tubing whereas it will not pinhole the tubing of the present invention having a stainless steel inner layer. Accordingly, the invention tubing has a much greater corrosion resistance than conventional copper tubing.

Stainless steel tubing itself has not been employed in applications such as the plumbing eld and the like due to the diiculty of soldering stainless steel itself; however, it has been discovered that when the stainless steel is coated with copper the composite tubing can be readily soldered and sweated into joints in the Very same manner and with the same ux solders as are today employed with usual copper tubing. Accordingly, the composite tubing of the present invention may be employed by a plumber with no difliculty and Without making any adjustments in the normal plumbing procedures. The composite tubing of the present invention can be used with the same sleeves, angles, valve housings and other coupling members as full copper tubing, and the joints made in the same way.

A novel method is also provided in the present invention for manufacturing the unique composite tubing as discussed hereinabove.

The provision of the composite tubing according to the present invention is particularly significant when it is considered that the cost of full copper tubing is continuously rising, and that stainless steel tubing of about .020 inch in thickness has approximately the same burst strength of full copper tubing of about .O80 inch in thickness. In addition stainless steel tubing is approximately 12 percent lighter than full copper tubing of the same thickness. The cost of the composite tubing of the present invention is less than one-half the cost of comparable copper tubing, thereby resulting in very substantial savings.

The completed composite tubing of the present invention includes the innermost corrosion resistant layer of 3,546,080 Patented Dec. 8, 1970 ice stainless steel having an intermediate layer of nickel electrolytically deposited thereon. This intermediate layer of nickel provides better adhesion with the outermost copper layer, thereby providing a superior finished product. Additionally, during the method of manufacture of the tubing, the layer of nickel plating passivates the stainless steel tube so as to reduce oxidation thereof until the final copper plating step of the process.

An object of the present invention is to provide new and novel composite tubing which can be used as a substitute in many applications for full copper tubing, and in particular which can be used in the plumbing eld with the same tittings and mounted in the same manner as full copper tubing.

Another object of the invention is to provide composite tubing which meets all the standards for full copper tubing, and yet which is considerably lighter for comparable applications.

Still another object of the invention is to provide composite tubing which can be substituted for full copper tubing and which is considerably less expensive and of no greater size.

A further object of the invention is the provision of composite tubing having greater corrosion resistance than comparable copper tubing.

A still further object of the invention is to provide a novel method of manufacturing composite tubing according to the present invention.

Other objects and many attendant advantages of the invention will become more apparent when considered in connection with the specication and accompanying drawings, wherein:

FIG. 1 is a longitudinal section through apparatus employed for carrying out an electrolytic depositing step of the present invention;

FIG. 2 is a top perspective view partly broken away illustrating the completed composite tubing according to the present invention; and

FIG. 3 is a sectional view taken substantially along line 3--3 of FIG. 2 looking in the direction of the arrows.

Referring now to the drawings wherein like reference characters designate corresponding parts throughout the several views, FIG. l illustrates apparatus employed in the present invention for electrolytically depositing nickel and copper on a stainless steel tube. A tank 10 is provided which contains a suitable solution 12 therewithin as described hereinafter. A pair of support members 14 and 16 are illustrated as mounted upon the sides of the tank, and these support members have bracket members 18 and 20 supported thereby. It will be understood that any suitable bracket or rack arrangement may be provided for supporting a desired number of tubes in the tank at any one time, a single tube being shown for the purpose of illustration.

These brackets 18 and 20 may be provided with suitable cutouts for supporting an elongated metallic rod 22 which is formed of iron or suitable electrically conductive. material. The opposite ends 24 and 26 of rod 22 are threaded. One end of the rod is provided with a threaded post 30 of reduced dimension having a nut 32 dispose thereon for clamping a contact 34 against the end of the rod, contact 34 being connected with a lead 36 to a suitable source of electrical energy.

A pair of stepped end plugs 40 and 42 are provided with central bores having threads formed therewithin whereby the end plugs are threaded on the opposite threaded ends of rod 22. These plugs 40 and 42 are adapted to t within a stainless steel tube 46 as illustrated. It will be noted as seen in FIG. 1 that the tube 46 is supported by the plugs 40 and 42 which have a iluid-tight seal therewith so lthat the solution within the tank cannot enter the interior of the tube.

Rod 22 is also provided with a plurality of radially outwardly extending members 50 which may be flexible metallic wires of electrically conductive material and which are arranged so as to define a substantially helical path about the rod 22. These members S are similar to the bristles provided on a conventional bottle washer. The outer ends of members 50 define a portion of a cylindrical surface of such a dimension that the outer ends of members S0 are adapted to engage the inner surface of tube 46 supported by the plugs and 42. Accordingly, members provide a substantially continuous electrical contact throughout the length of the inner surface of the stainless steel tube 46, members 50 also, of course, assisting in supporting the tube in operative position as illustrated.

It is apparent that when electrical energy is impressed upon lead 36, the electrical potential will travel along rod 22 and through the electrically conductive members 50 to the inner surface of tube 46 to thereby impress such potential upon member 46 throughout substantially the entire length thereof, thereby providing a very effective electrical connection with the tube.

In carrying out the method of the present invention, tube 46 is first mounted upon a rod 22 having end plugs 40 and 42 disposed thereon in the operative relationship shown in FIG. 1. The assembly of rod 22, end plugs 40, 42 and tube 46 is then immersed in a suitable cleaning bath which comprises a strong non-etch alkali bath for removing oils and soils therefrom. A typical cleaning solution may comprise Enbond S-61, manufactured by Enthone, Inc., of West Haven, Conn.

After the stainless steel tube has been cleaned with a suitable cleaning solution, it is removed from such bath and rinsed with fresh water.

The stainless steel tubing is then immersed in a nickel bath wherein the arrangement as shown in FIG. 1 is employed. The solution in the nickel bath may contain about 240 grams per liter of nickel chloride and about 36 grams per liter of hydrochloric acid. The tube is first made the anode of an electric circuit within the solution having nickel electrodes as cathodes in the usual manner. A current of about 120 amperes per square foot is then passed through the solution for about two minutes at a temperature of about F. The tube is then made the cathode and the nickel electrodes the anodes in the circuit, and a current is passed through the circuit at a current density of about 120 amperes per square foot for about two minutes until the desired layer of nickel is electrolytically deposited on the outer surface only of the stainless steel tube 46.

The tube is then removed from the nickel bath and rinsed with fresh water.

The tube is then immersed in a suitable copper bath. This copper bath may be either a cyanide or acid bath, or the two baths may be provided in sequence, that is, the tube may first be immersed in a cyanide copper bath and then in an acid copper bath.

An arrangement as shown in FIG. 1, is also employed in the copper bath. The solution of the cyanide copper bath may comprise about 27.5 grams per liter of cuprous cyanide, about 35.4 grams per liter of sodium cyanide, about 31.5 grams per liter of sodium carbonate, and about 31.5 grams per liter of Rochelle salt. A layer of copper is then electroplated on the nickel previously deposited on the stainless steel tube at a current density of about 50 amperes per square foot, while the solution is held at a temperature of about 120 F. until a suitable layer of copper is provided. The desired copper layer lies within a range of approximately 0.1 to 0.8 mil in thickness with an optimum thickness of approximately 0.2 mil.

If an acid copper bath is to be employed, the solution may contain about 200 grams per liter of copper sulfate and about grams per liter of sulfuric acid, and the electroplating may also be carried out at a current density of about 50 amperes per square foot until the desired coating of copper is obtained.

Referring now to FIGS. 2 and 3 of the drawings, the finished composite tubing is illustrated including an innermost continuous layer of stainless steel 46 defining a bore 58 therewithin which serves to conduct liquid therethrough when in use. An intermediate continuous layer 60 of nickel is electrolytically deposited on the outer surface of the tube 46, and an outermost continuous layer 62 of copper is electrolytically deposited on the intermediate layer of nickel 60.

It is apparent from the foregoing that there is provided according to the present invention a new and novel copper coated stainless steel tube wherein the composite tubing may be used as a substitute in many applications for full copper tubing and in particular may be used in the plumbing field with the same fittings and additionally may be mounted in the same manner as full copper tubing. The composite tubing of the present invention meets all standards required for full copper tubing and is at the same time considerably lighter. The tubing of the present invention is very economical in that its cost is substantially less than that of full copper tubing, and yet at the same time it is of no greater size. The completed tubing of the present invention provides greater corrosion resistance. A novel method is also provided for manufacturing the composite tube of the present invention, this method ensuring that the stainless steel tubing will be properly coated, and only on the outer surface thereof, while the inner surface of the stainless steel tube remains in its original condition.

As this invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, and Since the scope of the invention is defined by the appended claims, all changes that fall within the metes and bounds of the claims or that form their functional as well as conjointly cooperative equivalents are therefore intended to be embraced by those claims.

I claim:

1. The method of manufacturing composite tubing for use as a substitute for copper tubing and which can be used with the same fittings and mounted in the same manner as copper tubing, comprising providing a tube of stainless steel open at the opposite ends thereof, plugging the opposite open ends of said tube to provide a fluid-tight seal therewith, then cleaning said tube to remove oils and soils therefrom, then rinsing said tube, immersing said tube in a nickel bath and electrolytically depositing a layer of nickel thereon, then removing the tube from said bath and rinsing the tube, then immersing said tube in a copper bath and electrolytically depositing a layer of copper on said layer of nickel, whereby a composite tube is provided including an innermost continuous layer of stainless steel defining a bore therewithin having an intermediate continuous layer of nickel electrolytically deposited thereon and also including an outermost continuous layer of copper electrolytically deposited on said layer of nickel.

2. The method as defined in claim 1, wherein said nickel bath comprises a solution containing about 240 grams per liter of nickel chloride and about 36 grams per liter of hydrochloric acid, and wherein said tube is -first made the anode of an electric circuit having nickel electrodes as cathodes, passing a current of about amperes per square foot through said solution for about two minutes at a temperature of about 70 F., then making said tube the cathode and said nickel electrodes the anodes in said circuit, passing a current through said circuit at a current density of about 120 amperes per square foot for about two minutes to provide said layer of nickel.

3. The method as defined in claim 1, wherein said copper bath comprises a solution containing about 27.5 grams per liter of cuprous cyanide, about 35.4 grams per liter of sodium cyanide, about 31.5 grams per liter of sodium carbonate, and about 31.5 grams per liter of Rochelle salt.

4. The method as defined in claim 1, wherein said tube of stainless steel is supported on plugs fitting within opposite ends thereof, providing electrical contact with the interior of said stainless steel tube throughout the longitudinal extent thereof between said plugs, and applying electrical potential to said electrical contact when the tube is disposed within said nickel and copper baths respectively.

5. The method as defined in claim 1, wherein said nickel bath comprises a solution containing about 240 grams per liter of nickel chloride and about 36 grams per liter of hydrochloric acid, said tube irst being made the anode of an electric circuit having nickel electrodes as cathodes, passing a current of about l2() amperes per square foot through said solution for about two minutes at a temperature of about 70 F., then making said tube the cathode and said nickel electrodes the anodes in said circuit, passing a current through said circuit at a current density of about 120 amperes per square foot for about two minutes until said layer of nickel has been deposited 0n the tube, said copper bath comprising a solution containing about 27.5 grams per liter of cuprous cyanide, about 35.4 grams per liter of sodium cyanide, about 31.5 grams per liter of sodium carbonate and about 31.5 grams per liter of Rochelle salt, and electrolytically depositing a layer of copper on said layer of nickel, the

layer of copper being within the range of approximately 0.1 to 0.8 mil in thickness.

References Cited UNITED STATES PATENTS 950,777 3/1910 Winslow 204-25 962,655 6/1910 Murphy 204-25 2,973,307 2/1961 Hahn 204-34 3,475,285 10/ 1969 Scavullo 204--25 FOREIGN PATENTS 469,681 7/1937 Great Britain 204-9 OTHER REFERENCES Deposition of Metals Upon Stainless Steel, Joseph Haas and Elmer Unruh, The Metal Industry, November 1925, p. 451.

JOHN H. MACK, Primary Examiner 20 T. TUFARIELLO, Assistant Examiner U.S. Cl. X.R. 204-34, 40 

1. THE METHOD OF MANUFACTURING COMPOSITE TUBING FOR USE AS A SUBSTITUTE FOR COPPER TUBING AND WHICH CAN BE USED WITH THE SAME FITTINGS AND MOUNTED IN THE SAME MANNER AS COPPER TUBING, COMPRISING PROVIDING A TUBE OF STAINLESS STEEL OPEN AT THE OPPOSITE ENDS THEREOF, PLUGGING THE OPPOSITE OPEN ENDS OF SADI TUBE TO PROVIDE A FLUID-TIGHT SEAL THEREWITH, THEN CLEANING SAID TUBE TO REMOVE OILS AND SOILS THEREFROM, THEN RINSING SAID TUBE, IMMERSING SAID TUBE IN A NICKEL BATH AND ELECTROLYTICALLY DEPOSITING A LAYER OF NICKEL THEREON, THEN REMOVING THE TUBE FROM SAID BATH AND RINSING THE TUBE, THEN IMMERSING SAID TUBE IN A COPPER BATH AND ELECTROLYTICALLY DEPOSITING A LAYER OF COPPER ON SAID LAYER OF NICKEL, WHEREBY A COMPOSITE TUBE IS PROVIDED INCLUDING AN INNERMOST CONTINUOUS LAYER OF STAINLESS STEEL DEFINING A BORE THEREWITHIN HAVING 